The semiconductor integrated circuit (IC) industry has experienced rapid growth. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. However, such scaling down has also been accompanied by increased complexity in design and manufacturing of devices incorporating these ICs, and, for these advances to be realized, similar developments in device fabrication are needed.
As merely one example, advances in lithography have been important to reducing device size. In general, lithography is the formation of a pattern on a target. In one type of lithography, referred to as photolithography, radiation such as ultraviolet light passes through or reflects off a mask before striking a photoresist coating on the target. Photolithography transfers a pattern from the mask onto the photoresist, which is then selectively removed to reveal the pattern. The target then undergoes processing steps that take advantage of the shape of the remaining photoresist to create features on the target. Another type of lithography, referred to as direct-write lithography, uses a laser, an electron beam (e-beam), ion beam, or other narrow-focused emission to expose a resist coating or to pattern a material layer directly. E-beam lithography is one of the most common types of direct-write lithography, and, by directing a collimated stream of electrons to the area to be exposed, can be used to remove, add, or otherwise change a material layer with remarkable accuracy.
In order to pursue even smaller critical dimensions (CD) of device features, multiple lithographic patterning iterations may be performed in order to define a single set of features. However, because of the complex interactions between the lithographic iterations, many such processes involve strict design rules specific to the lithographic techniques to be used. Design rules associated with a particular lithographic flow may not be acceptable for all designs. Therefore, while existing lithographic techniques have been generally adequate, they have not proved entirely satisfactory in all respects. Improved techniques for multiple patterning may relax existing design rules, overcome existing limitations, and thereby enable even more robust circuit devices to be manufactured.